Ultrastructural analyses using a variety of experimental approaches are central to ongoing and proposed studies within the laboratories of the primary user groups participating in this shared instrumentation proposal. The primary user group consists of five, highly interactive, NIH-funded laboratories (Mooseker, Forscher, Pollard, Rosenbaum and Wells), all of which are members of the Department of Molecular, Cellular and Developmental Biology (MCDB), Yale University. The long term objective of this proposal is to upgrade/replace the transmission electron microscopy (TEM) equipment currently housed in the MCDB EM facility. This well established facility, maintained and operated by a full time, highly skilled EM technician/instructor, provides both research and training support to the research laboratories in MCDB. The principal investigator and four co-investigators represent the current major research groups using this facility, although a number of other laboratories from several departments also use this facility. Unfortunately, the existing TEMs and ancillary support equipment in this facility are quite old and maintenance due to lack of replacement parts will soon render this facility inoperable. As a consequence, the NIH-funded research projects of the user group, all of which employ ultrastructural analyses, are in jeopardy. The research goals of the user group all focus on structural, biochemical and functional analyses of a wide range of components of the eukaryotic cell cytoskeleton. TEM is used for a broad scope of investigations, from ultrastructural studies on purified cytoskeletal (both actin-filament and microtubule associated) components, isolated organelles, cells and tissues, including cells with altered cytoskeletal functions resulting from mutations in various cytoskeletal components. The requested TEM equipment is essential for the research objectives of the user group, and will also provide much needed research support for the broader research community at Yale.